Kaptan boat with 9.9 yamaha vs 15 Evenrude

[bigboy]

Guys i have a really big dillema and also am a bit worried. We just got a 13ft Kaptan boat powered by a 9.9 yamaha. On my Albatross i have an Evenrude 15hp and we decided to try it out on the kaptan. The results we got were really worrying and shocking. With the 9.9 it was giving a clear 16.5 knots with 2 persons and with the 15 it gave us 14.2 knots with the same load.

We were waiting that with the 15 it would do at least 20 knots because it is much more pwerful than the yamaha. Could it be i have some sort of trouble in my engine or what  Btw they are both long shaft.

Help from you guys would be kindly appreciated.

[benri]

Is the propellor pitch the same? 99.9% the only reason is that you need a different propellor on the bigger motor for the Kaptan.

[shanook]

i had a kaptan 13ft and i used to do 18knots with a 9.9 Force. u should do better with a 15hp. kaptan boats plane a lot better than other boats

[visa]

big boy first check if the 9.9hp is opened to 15hp this is oftern done so that the owner is not made to regester the 9.9hp i had one and used to push my 19ft boat at around 7/8 knots. and most probely htats the reason. Have fun and dont worry about your 15hp it could be that it just needs a better propeller as benri suggested.

[busumark]

most probably the 9.9 is changed to 15hp but basically they are the same engine there isnt a lot of difenrence between them

[bigboy]

no it is not changed. It is a 9.9.

[skip]

On the basis that a 15hp is probably factory propped to push a heavier boat I would say off hand you don't have enough pitch on the prop. Have a look at the stamping on the prop of both and let us know. You're looking for something like 9.3 x 8 for example.

If you connected a rev counter temp to the 15 you'd probably find you are at the top end of its WOT, so you're not getting that extra power without putting a more aggresive pitch.

[bigboy]

Skip what does WOT mean please? i will try get the size and pitch numbers of the propellers tonight. Thanks very much for your help it is much appreciated

[skip]

WOT is Wide Open Throttle and it's a range specified by the manufacturer to indicate the ideal maximum engine operating range, probably something in the region of 5200-5800rpm for your engine. The WOT is used as a guide to select the correct pitch allowing the engine to sit comfortably in that range.

If I were testing the boat on my own with a lightish load I would be looking to be at the top end of the WOT, ie 5800rpm so that when you then add some people and equipment you will sit comfortably in the middle of that range.

It's important that you have the rpm guage so you know where you are.

[bigboy]

Skip where can the RPM gauge be connected to please ?

[skip]

It has to go into the wiring loom within the engine where there should be a connector. I need to investigate the same thing with mine in order to check it as well.